1. Field of the Invention
The present invention relates to a multilayer wiring board having two or more wiring layers and a manufacturing method thereof. More specifically, this invention relates to the multilayer wiring board and the manufacturing method thereof having the step of forming an upper wiring layer, a part thereof being electrically connected with a pillar-like metallic body, after the pillar-like metallic body is formed on a lower wiring layer.
2. Description of the Related Art
In recent years, as electronic equipiments and the like are miniaturized and light-weighted, electronic parts are miniaturized and wiring boards onto which the electronic parts are mounted are required to be higher density, In order to heighten the density of the wiring boards, a method of heightening line density of wiring layers or a method of obtaining a multilayer structure by laminating a plurality of wiring layers are adopted.
The method of manufacturing a multilayer wiring board includes a joining method of forming wiring layers respectively on a plurality of substrates and joining the substrates in a state that insulating sheets intervene between the substrates, and a build-up method of forming insulating layers on a substrate on which a wiring pattern is formed and forming the wiring pattern on the insulating layer, namely, of forming a laminated structure by repeating formation of the insulating layers and wiring patterns. However, since the latter build-up method is advantageous to the heightening of the density of the wiring boards, this method is becoming the mainstream.
Meanwhile, in the multilayer wiring board, conductive connection between the wiring layers should be carried out according to a circuit design. Such conductive connection have adopted an conductive connecting structure that au opening portion of an insulating layer which is called as a via hole is plated cylindrically. However, as for the via hole, when the opening portion is formed and plated, there arises problems that fine processing is difficult and air becomes contaminant. For this reason, in the case where reliability of the wiring board is maintained, the size of the via hole is limited. Moreover, when multilayer are laminated, it is difficult to form a via hole just above a via hole, and the design of the laminated structure is restricted. For this reason, the heightening of the density of the multilayer wiring boards is limited.
On the contrary, in the method of the wiring layers are electrically connected by a pillar-like solid conductor, there does not arise such a problem. For this reason, this method can further heighten the density of the multilayer wiring boards in comparison with the case where a via hole is formed Therefore, it is estimated in this field that the conductive connection between the wiring layers by means of the pillar-like conductor will become the mainstream in the future, and a lot of methods of forming pillar-like conductors are suggested.
For example, Japanese Patent Application Laid-Open No. 9-23065 discloses a method of forming an opening portion on an insulating layer provided on a lower wiring layer by means of laser processing or the like and carrying out electroless plating on the opening portion and filling a pillar-like conductor into the opening portion. Moreover, Japanese Patent Application Laid-Open No. 6-314878 discloses a method of wholly conducting a lower wiring layer and forming a resist pattern having an opening portion and depositing metal on a concave section of the resist pattern by means of electrolytic plating to form the pillar-like conductor.
However, both the above methods have a problem that a height of the pillar-like conductor is easily non-uniform. The former method has a problem that it takes a long time to form the pillar-like conductor because the electroless plating is carried out. The latter method has a problem that current density cannot be heightened and similarly the formation of the pillar-like conductor takes a long time because the electrolytic plating is carried out. Further, the formation of a resist pattern requires a large-scale apparatus for emitting a laser, and thus these methods are disadvantageous from the viewpoint of costs. Further, since it is difficult to securely remove a resist on a bottom portion of the opening portion, reliability of conducting of the pillar-like conductor is lowered.
Therefore, it is an object of the present invention to provide a multilayer wiring board and a manufacturing method thereof which are capable of manufacturing a multilayer wiring board with a combination of simple facility and conventional process and thinning lines of the wiring layer and which have high reliability of the wiring board.
The above object can be achieved by the following invention. Namely, a multilayer wiring board manufacturing method of the present invention having the step of forming a pillar-like metallic body on a lower wiring layer, and then forming an upper wiring layer, a part thereof being electrically connected with the pillar-like metallic body, is characterized in that the pillar-like metallic body forming step includes: the step of forming a plating layer of metal constituting the pillar-like metallic body; the step of forming a mask layer on a surface portion of the plating layer where the pillar-like metallic body is formed; and the step of etching the plating layer.
According to the manufacturing method of the present invention, since the plating layer is formed not in the opening but on the whole surface and the pillar-like metallic body is formed by etching, laser emission or the like is not particularly required, and a diameter of the pillar-like metallic body can be reduced. Further, since the opening section from which the resist is removed is not plated, the reliability of conductivity between the lower wiring layer and the pillar-like metallic body is heightened. As a result, manufacturing can be carried out by simple facility and combination of conventional steps, and the multilayer wiring board, wherein the wiring layer can be thinned and the reliability of the wiring board is high, can be manufactured.
The manufacturing method of the present invention includes the following first through fourth embodiments.
In the first embodiment, the pillar-like metallic body forming step includes the steps of:
(1a) coating an approximately whole surface of said lower wiring layer including a non-patterned portion with another metal showing resistance at the time of etching the metal constituting said pillar-like metallic body to form a protective metallic layer,
(1b) forming a plating layer of the metal constituting said pillar-like metallic body on an approximately whole surface of said protective metallic layer by means of electrolytic plating;
(1c) forming a mask layer on a surface portion of said plating layer where said pillar-like metallic body is formed;
(1d) etching said plating layer; and
(1e) etching under condition wherein at least said protective metallic layer can be corroded to remove at least said protective metallic layer covering the non-patterned portion
According to the manufacturing method of the first embodiment, since the protective metallic layer is provided, the lower wiring layer is not corroded at the time of etching the plating layer, and the desired pillar-like metallic body can be formed in the position where the mask layer is formed. Further, after the step (1d), the protective metallic layer remaining on the non-patterned portion can be removed securely by the step (1e), and the protective metallic layer under the pillar-like metallic body is hardly corroded at the step (1e). For this reason, short circuit between pattern portions hardly occurs, the reliability of the wiring board is heightened, and thinning is possible. Further, since the protective metallic layer is formed on the whole surface, the plating layer can be formed by electrolytic plating. Moreover, since the plating layer is formed in the hole but on the whole surface, the plating layer having a desired thickness can be formed for a short time with high current density.
In the above manufacturing method, it is preferable that the step (1a) executes electroless plating on the whole surface of the previously patterned lower wiring layer including the non-patterned portion so as to form a base conductive layer and further executes electrolytic plating on the approximately whole surface so as to form the protective metallic layer, and the step (1e) executes the etching under condition wherein said protective metallic layer can be corroded and then removes said base conductive layer remaining on the non-patterned portion by means of soft etching.
In this case, since the electroless plating is previously carried out on the whole surface so that the base conductive layer is formed, this can be a plating-use electrode, and the protective metallic layer can be formed suitably by electrolytic plating. Such electrolytic plating is preferable because electroless plating occasionally makes it difficult to etch the protective metallic layer due to mixing of component other than metal. Moreover, since the base conductive layer remaining on the non-patterned portion is removed by soft etching, short circuit between pattern portions is prevented, so that the reliability of the wiring board can be further improved.
In addition, it is preferable that the step (1a) executes electroless plating on an approximately whole surface of an insulating layer so as to form a base conductive layer and then executes electrolytic plating on an approximately whole surface of the patterned lower wiring layer on the base conductive layer so as to form the protective metallic layer, and the step (1e) executes etching under the condition wherein the protective metallic layer can be corroded and then removes the base conductive layer remaining on the non-paned portion by means of soft etching.
In this case, similarly to the above, the protective metallic layer can be formed suitably. Moreover, the reliability of the wiring board can be further improved.
In addition, it is preferable that prior to the step (1a), an insulting layer having the approximately same thickness as a patterned portion of the lower wiring layer is formed on the non-patterned portion of the lower wiring layer so that the surface is flattened, In this case, since the protective metallic layer formed at the step (1a) is flattened, the protective metallic layer can be removed securely at the step (1e), and short circuit between patterns or the like can be prevented securely.
In the above method, it is preferable that the metal constituting the pillar-like metallic body is copper and another metal constituting the protective metallic layer is gold, silver, zinc, palladium, ruthenium, nickel, rhodium, lead-tin solder alloy or nickel-gold alloy. In this case, the pillar-like metallic body can be cheaply formed by copper having good conductivity by the general-purpose etching method. Moreover, since the metal constituting the protective metallic layer shows good resistance for etching, the reliability of the wiring board can be maintained high.
A multilayer wiring board of the present invention is obtained by the manufacturing method of the first embodiment and has a structure that a lower wiring layer and an upper wiring layer are electrically connected, the structure comprising the lower wiring layer, a protective metallic layer provided on a part of an upper surface of the wiring layer, a pillar-like metallic body provided on a whole upper surface of the protective metallic layer and the upper wiring layer, a part 1 thereof being electrically connected with the pillar-like metallic body. The multilayer wiring board of the present invention can be manufactured by simple facility and combination of the conventional steps, and the wiring layer can be thinned, and the reliability of the wiring board becomes high.
In the manufacturing method of a second embodiment, the pillar-like metallic body forming step includes:
(2a) forming a conductive layer on a surface of a metallic panel layer provided on an approximately whole surface of an insulating layer, the conductive layer having resistance at the time of etching the metallic panel layer and the same pattern as said lower wiring layer;
(2b) forming a plating layer of metal which can be etched simultaneously as said metallic panel layer on an approximately whole surface of said metallic panel layer with said conductive layer;
(2c) forming a mask layer on a sure portion of said plating layer where said pillar-like metallic body is formed; and
(2d) etching said metallic panel layer and said plating layer so as to form said lower wiring layer and said pillar-like metallic body.
According to the manufacturing method of the second embodiment, after the conductive layer to be etching resist is formed on the surface of the metallic panel layer, the plating layer and the mask layer for forming the pillar-like metallic body are formed and etching is carried out. For this reason, when the metallic panel layer and the plating layer are corroded, the pillar-like metallic body and the patterned wiring layer and conductive layer remain. Therefore, since the pillar-like metallic body can be formed and simultaneously the wiring layer can be formed, a number of steps and time required for all the steps can be reduced and simultaneously load in the steps can be reduced. Moreover, since the conductive layer which intervenes between the pillar-like metallic body and the lower wiring layer is conductive, the pillar-like metallic body and the wiring layer can be electrically connected.
In the above manufacturing method, it is preferable that the step (2a) coats the metallic panel layer with a photosensitive resin layer and pattern-exposes and develops so as to remove a portion where the conductive layer is formed, and plates the removed portion with metal so as to form the conductive layer.
In this case, the conductive layer of the present invention can be formed by the same method as the case of forming a conventional wiring layer in simple general-purpose facility. At this time, since the metallic panel layer to be a base is conductive, electrolytic plating can be carried out so that adhesion with the wiring layer to be formed can be heightened.
In addition, it is preferable that the metal constituting the metallic panel layer and the plating layer is copper, and the metal constituting the conductive layer is gold, silver, zinc, palladium, ruthenium, nickel, rhodium, lead-tin solder alloy or nickel-gold alloy, In this case, the lower wiring layer and the pillar-like metallic body can be formed by copper having good conductivity at low cost by the general-purpose etching method, and the metal constituting the conductive layer shows good resistance for the etching. For this reason, the reliability of the wiring layer can be maintained high.
A multilayer wiring board of the present invention is manufactured by the manufacturing method according to the second embodiment. Similarly to the first embodiment, the multilayer wiring board can be manufactured by simple facility and combination of conventional steps, the wiring layer can be thinned, and the reliability of the wiring board becomes high.
In the manufacturing method of a third embodiment, the pillar-like metallic body forming step includes the steps of:
(3a) forming a protective layer, in which a portion where said pillar-like metallic body is formed is made of a conductor and the other portion is made of an insulator, so that said protective layer covers an approximately whole surface of said lower wiring layer,
(3b) forming a plating layer of metal constituting said pillar-like metallic body on an approximately whole surface of said protective layer;
(3c) forming a mask layer on a surface portion of said plating layer where said pillar-like metallic body is formed; and
(3d) etching said plating layer.
According to the manufacturing method of the third embodiment, since the above protective layer is provided, the lower wiring layer is not corroded at the time of etching the plating layer, and the pillar-like metallic body having a desired shape can be formed in a desired position. At this time, since the conductive portion is formed on the protective layer, the lower wiring layer and the pillar-like metallic body can be conductive. Moreover, since the patterned portion of the wiring layer is coated mainly with an insulator, a possibility of short circuit between patterns is small, and the reliability becomes high and thinning is possible. Moreover, since metal for protecting the patterns is not much required, this is advantageous to the cost.
In the above manufacturing method, it is preferable that the step (3a) coats the lower wiring layer with a photosensitive resin layer, and pattern-exposes and develops so as to open the portion where the conductor is formed, and plates the opened portion with metal so as to form the protective layer. In this case, the protective layer having high reliability can be formed by comparatively simple step and a low-priced apparatus.
In addition, it is preferable that when the opened portion is plated with metal, electroless plating is carried out by using the metal constituting the lower wiring layer as a catalyst. In this case, the conductor having a desired thickness can be formed selectively on the opened section.
A multilayer wiring board of the present invention is manufactured by the manufacturing method according to the third embodiment. Similarly to the other embodiments, the multilayer wiring board can be manufactured by simple facility and combination of conventional steps, the wiring layer can be thinned, and the reliability of the wiring board is high.
Another method of manufacturing a multilayer wiring board includes the step of forming a pillar-like metallic body on a topmost wiring layer by means of the above step of forming a pillar-like metallic body. Such a pillar-like metallic body is formed for mounting or the like of chip parts, but similarly to the case of the pillar-like metallic body between the wiring layers, the pillar-like metallic body having high density and reliability can be formed by simple facility and combination of conventional steps,
In addition, in another multilayer wiring board of the present invention, a pillar-like metallic body is formed on a topmost wiring layer by means of the above step of forming a pillar-like metallic body.